Their candidate, Mohamed Morsi, looks likely to become president, but the military, which has stifled Islamists for years, is sharply tightening its grip.

CAIRO — With his hands chained and raised toward the sky, Ahmed Elsayed Attia stood chanting in the heart of Tahrir Square with dozens of fellow Muslim Brotherhood supporters against Egypt's military rulers.

Referring to the Supreme Council of the Armed Forces, or SCAF, as "thieves" bringing Egypt to its knees, Attia, a state employee earning no more than $150 a month, lifted his metal chains as a symbol of despair for him and his nation.

On the other side of the vast square, a sparse crowd of about 100 Islamists celebrated and chanted, "Here is the president." They pointed to pictures of Muslim Brotherhood candidate Mohamed Morsi, who is projected to have defeated Ahmed Shafik, an ally of toppled leader Hosni Mubarak, in the weekend's runoff election.

The numbers are not official, but Egyptian media reported that the Brotherhood believed Morsi had won 52.5% of the vote. Shafik, Mubarak's former prime minister, was seen as the military's candidate of choice. Media reports said Morsi was ahead by about 1 million votes.

"I can't describe how happy I am to be standing here after 60 years of darkness under Mubarak and his military rule," said Abdallah Mahmoud, a schoolteacher, as he stood in the bright sun proudly waving a photo of Morsi.

Members of the Brotherhood wavered between elation and anger throughout much of the day. The likelihood that Morsi will become president moves Egypt a tantalizing step closer to the organization's 84-year-old goal of instilling political Islam in the government. At the same time, the military, which has backed a state that has imprisoned Islamists for decades, sharply tightened its grip on the country's political system over the weekend.

Egypt's ruling military council issued a temporary constitutional declaration that greatly limits the powers of the presidency. The declaration also gives the military council the right to form Egypt's constituent assembly, which will be responsible for writing the constitution by the end of the year. It also continues to keep the military budget from civilian oversight.

"With the new constitutional declaration issued by SCAF tonight [Sunday], Egypt has completed its full transition into a military dictatorship," Hossam Bahgat, a human rights advocate working with the Egyptian Initiative for Personal Rights, said on his Twitter account.

As Brotherhood supporters in Tahrir praised Morsi, they also warned of possible confrontation with the army if the constitutional declaration is not revoked and power handed to the newly elected president.

"The only legitimacy goes to the elected president! They want to rule the country and the president even after leaving!" Mahmoud yelled. "We won't accept this and we will be in the streets to take back our rights!"

The Muslim Brotherhood along with the April 6 Youth Movement and other revolutionary powers also called for mass demonstrations on Tuesday.

"The military wants the president to be like an employee for them. This declaration is completely unacceptable," said Hassan Abdelghany, a spokesman for the electoral campaign of the Freedom and Justice Party, the political arm of the Muslim Brotherhood.

The military's action came days after Egypt's Supreme Constitutional Court dissolved the recently elected Islamist-dominated parliament. Some Brotherhood members suggested that the upended legislators might convene in Tahrir until the military unlocked parliament.

Abdelghany said the Freedom and Justice Party would meet with several political parties to discuss the military's actions as well as demand a new constitutional decree drafted by the people.

"The parliament, which was chosen by the people, was supposed to form the constituent assembly. Now the SCAF will," he said. "We will decide what action we will take regarding this crisis after the official results of the elections are announced."

For now, however, Abdelghany said the Brotherhood would join in street protests to pressure the military to revoke its declaration.

"We have plans to be in the street," Abdelghany said. "The only solution at this point is for the military to leave power completely and return to their barracks."

Abdellatif is a special correspondent. Times staff writer Jeffrey Fleishman contributed to this report.